Partial aortic occlusion and cerebral venous steal: venous effects of arterial manipulation in acute stroke.

Acute ischemic stroke therapy emphasizes early arterial clot lysis or removal. Partial aortic occlusion has recently emerged as an alternative hemodynamic approach to augment cerebral perfusion in acute ischemic stroke. The exact mechanism of cerebral flow augmentation with partial aortic occlusion remains unclear and may involve more than simple diversion of arterial blood flow from the lower body to cerebral collateral circulation. The cerebral venous steal hypothesis suggests that even a small increase in tissue pressure in the ischemic area will divert blood flow to surrounding regions with lesser tissue pressures. This may cause no-reflow (absence of flow after restoration of arterial patency) in the ischemic core and "luxury perfusion" in the surrounding regions. Such maldistribution may be reversed with increased venous pressure titrated to avoid changes in intracranial pressure. We propose that partial aortic occlusion enhances perfusion in the brain by offsetting cerebral venous steal. Partial aortic occlusion redistributes blood volume into the upper part of the body, manifested by an increase in central venous pressure. Increased venous pressure recruits the collapsed vascular network and, by eliminating cerebral venous steal, corrects perifocal perfusion maldistribution analogous to positive end-expiratory pressure recruitment of collapsed airways to decrease ventilation/perfusion mismatch in the lungs.